This invention relates to a negative pressure generating system for vehicles powered by internal combustion engines.
Conventionally employed as a negative pressure source for operating a brake booster in an internal combustion engine powered vehicle was the negative intake pressure in the engine, a vacuum pump, or the like, so that there were such drawbacks as insufficient negative intake pressure in the engine and increases in cost, space, weight and so forth along with the installation of a vacuum pump.
Meanwhile, the air discharged from the air pump was let out into the atmospheric air when unnecessary, for example, when the rotating speed of the engine decreased abruptly, or the discharged air was recirculated to the suction port of the air pump or otherwise wastefully treated.